it all began early in the evening with a shooting in cambridge, massachusetts, where an m.i.t. campus police officer was shot and killed. we are going to continue to follow this big breaking story, of course, stay with us for continuing coverage. this story. stay with us for continuing coverage. we continue to cover this breaking news out of the boston, massachusetts, area. officials believe that there is a strong possibility that they have now zeroed in on the suspects related to the boston marathon bombings. it all began with a sequence of events last night. it started with a shooting on the campus of m.i.t. where a m.i.t. campus police officer was

responding to a report of disturbance where he was shot multiple times and killed. then, an outbust in watertown, two suspects engaged in a firefight with law enforcements. witnesses reported hearing at least three blast. one eyewitness we spoke to said that he saw the suspects tossing what appeared to be hand grenaded and a pressure cooker bomb at law enforcement officials. i want to bring now in nbc's justice correspondent pete williams live in washington now. >> reporter: well a couple of things. number one, we have heard that one police officer was killed earlier tonight. and now, we hear there may have been a second police officer killed. we have one report about that. as for the two people who were

arrested tonight -- or the two, let's use the suspects related to this incident here, we know that one is in custody, and we believe now that we have had at least one report that the other, authorities up there, may be dead. i think they're trying to confirm that now. they don't know for sure. and that's one of the reasons you earlier saw that report that they wanted people to stay in their homes and lock their doors. another possibility is they're looking for a third suspect. i think that, as more little bit of information come in here, the scale is tipping more and more in the direction of that these arrests are -- or this action tonight is related to the boston bombings.

and we're just waiting to get some confirmation here. just a growing sense here that's what going on here. >> pete you shared a number of the factors that are tipping the scale in that direction, can you recap why law enforcement think that this may be in fact be row lated to the boston bombings? >> yes. once we get -- once they get the names and a better look at them, my impression is from talking to a couple of sources, there's at least one person in custody, does that person look like one of the people in the pictures that's one thing they will be trying to answer. i'm going to guess here, one of the reasons why the sort of sense in law enforcement is that they're related the feeling is that the answer to that question

is yes. back to the earlier thing that you asked about, the factors here, it's worth repeating that this did not start with the fbi going out and trying to arrest someone for started the boston bombing. it was something that started to escalate into this night of shootings and explosions in watertown, in at least one or two police officers were killed. interest by the fbi in people in this area, that's number one. so, it's not as though there wasn't an interest by fbi for folks in that area. suggestion number two is, that both eyewitnesses and law enforcement officials have said as things settled down, you could see a pressure cooker and a suggestion that it was a pressure cooker device on the street up there, that one of these suspects may have tried to

deploy and that's important, because one and two possibility two of the bombings used in the boston bombing was built in a pressure cooker and number three, there was a name of a person that they were trying to find who initially we were told may have been one of the people in custody, we're not quite so certain right now. we're still trying to figure what the names are. but there's several factors now that i think suggest and i can tell you, i'm getting the same sense that john is getting from the people that he's talking to that there's a connection here. >> we heard pretty much from the beginning they were looking for two suspects, are you hearing anything different, that there may be other people who may have been aiding these people? >> reporter: we have to be careful of the word suspects, that's the term that the fbi

used for the two people they were seeking, that set of suspects number one. and then we have the people who are arrested tonight and are in custody for the thing in watertown. i don't know if there's a third person they're looking for in watertown. they're telling people up there to keep their doors locked. that's why i'm guessing there may have been a third. but i don't know. >> pete williams in d.c., thanks so much for that. we heard from pete williams officials have one person in custody and there may be a second person who is a dead and there may be a third person at large. we don't want to use the term suspect inaccurately. as pete noted, there's some kind of ongoing threat in the area. this all began last night when

witnesses reported hearing a number of explosions in watertown, massachusetts, at least three explosions, we heard that from a number of different witnesses. we also heard reports of firefights. one eyewitness telling us that there were too many gun shots to count. reports of evacuations of residents as that began to unfold. we heard from an eyewitness who saw the whole thing from his apartment. he said that it went on for quite some time and he saw a pressure cooker and hand grenade being thrown on the street. as these events have progressed, reporting has revealed that it's increasingly likely that in fact these suspects are in some way connected to the boston marathon

bombings, there were a number of factors that's tipping the scale in that direction. those bombings took place on monday, two explosions took place on monday. killing three and injuring 170. yesterday, officials released photos of the individuals they believed responsible for those attacks. two gentlemen. they didn't have the names of the people that they were looking for. they had those photos. they report edly received thousands of tips, phone calls and information. we don't know how all of this ties together. we don't know if this is tied in fact to the shooting at m.i.a. last night which was the first case of violence at m.i.t. we are in fact starting to believe at this point, based on our reporting that the violence in watertown is in fact connected to the bomb blast at the boston marathon. i want to go live now to lester

holt who is in watertown with the very latest on the ground there. >> let's walk folks through the events. it began last evening with this disturbance at m.i.t. that required a police response. the police officer was met with several shots, he was shot and killed. a search along the river bank and a transit station across the river in boston. we're then told at some point in the evening the suspect believed from that shooting car jacked a vehicle from near a gas station and led police on a chase here to watertown, about four miles away, at some point in that chase, as police came over here, they were confronted with gunfire, we heard from some video that was shot by a resident, a prolong volley of gunfire, an exchange back and forth. an witness who was watching from his window described watching

this activity, watching the two men firing at police, taking cover behind an suv and even throwing explosives in the direction of police. he described them as grenade-like devices. nevertheless, one of the suspects is reportedly has been taken into custody, perhaps shot, the other one had managed to blast through the police barricade in a vehicle and is believed to be at large. want to go to pete williams who's been working his sources. pete, by this point, it's been widely concluded that this is in fact related to the bombings of monday. the question is, are the two men confronted today the same ones we saw that in that photo? >> reporter: it does appear that the answer is yes. two law enforcements firnls have

told us that the incident did involved the two men who are the suspects in the boston bombing. one is dead. the other is at large. the person who set the bomb they believe at the second bombing site at the boston marathon is at large. the so-called "white hat" suspect. let's repeat this lester. we have been twoeld independent law enforcement officials that the whole thing tonight in watertown involves the two people whose pictures were shown by the fbi, the two people the fbi believes were the boston marathon bombers. one they say is dead and the other is at large. the so-called "white hat" suspect. this is the that person you just saw, the one with the black hat, we believe is dead. the person with the white hat,

who set the bomb at the second bombing location, is the person that is said to be at large. authorities consider him armed and dangerous. the watertown police earlier sent out a note to their residents saying stay at home. bliss believe this person is out there. >> have they learned or discovered about whether this was a cell or some kind, this residence in watertown, connected to a larger cause or organization? >> don't know the answer to that. >> we heard from nbc's kerry sanders a few minutes ago who was watching the activities of s.w.a.t. teams. metal detectors were set off in a building. several blocks of watertown are

sealed off right now as police take control of the crime scene area and obviously try to find this other suspect. pete, let me ask you, as you just confirmed that the two men in the pictures are the two men involved here tonight. i had heard from another police officer here who was just briefing reporters casually suggesting that they might be looking for others. have you heard anything else? >> i don't believe that's the case now. this is becoming more and more clear, they are looking for someone. our sense is, there were just two people involved here. again, the caveat that this is a fluid situation and our understanding of this changes every 15 minutes. the person you're looking at now the so-called "black hat" suspect from the boston bombing is dead. and that the white hat suspect is at large. they are trying to find him, and

so we believe they're just two people. >> the fact that this began in cambridge at m.i.t. where that police officer was shot, any suggestion that they were targeting m.i.t., any idea one or both of those suspects would have been on that campus? >> no, i think it's becoming more and more clear now, even as the fbi had a news conference tonight, or last night rather, and said they weren't sure of the identities they had some names in mind based on their own investigative work. their interest was already high in this paert of massachusetts of some names of people in that area. so, they were not just -- we believe, not just throwing the pictures out there with no clue at all what the names were, they did have some ideas.

what precisely what they were we don't know. >> all right, pete williams with a mayor development here. that the two men involved in the shootout here in watertown are in fact, according to fbi officials, the two men who were seen in those photos released yesterday. mara? >> right now, i want to bring in correspondent jonathan dean, who has been working his law enforcement sources on this story. >> i can echo some of what pete reported. i can confirm one suspect dead and the search continues for a second. that according to two law enforcement sources. as pete is saying, it appears that his officials say that there's now this defen tif link to the link to the bomb suspects. i'm told that it is a strong

possibility given the visual and physical evidence that has been recovered at these multiple crime scenes. and i'm still waiting to hear that definitive information. but, as evidenced from the massive response and the unbelievable set of incidents that took place here this evening and the fbi now out in full force, investigating and tracking this second suspect, it appears a very strong possibility that these two incidents are linked, both tonight's, overnight chaos with the killing of a police officer and the shootings that took place and the bombing at the boston marathon. so -- >> jonathan, do we know -- now, we have a strong belief that these men are linked to the bombing, were they the ones in

the photos released yesterday? >> yes. if pete, from his sources saying that the white hat and black hat suspects have been identified and one is dead and the other one is still being sought and he has that from multiple sources out of the justice department or fbi, they're confident they got their man. the issue is now, with the names that we have, we're just waiting for them to put them out officially to say these are the guys, these were the men we're looking for, we have now confirmed that, we haven't received that yet. we're waiting on that. again, they were matching actual people to video clips. and that work takes some time. especially with the description that i have of the deceased

suspects that there were multiple gunshot wounds. i'm told that he was shot numerous times and he is deceased. a formal identification may take some time or perhaps it may have been completed. again, meanwhile, the man hunt continues for the second suspect who apparently broke through some sort of check point and standoff with police early this morning during this shootout and chase and is still on the loose and local police and federal officials are in the process of trying to hunt him down and find him. >> all right, jonathan, we'll come back to you to see what you're hearing. this all of course began to unfold last night with reports of explosions and gunfire in watertown, massachusetts, that's in the boston area, we want to take a minute now to watch some

home video that was shot of that firefight as it was taking place. let's take a listen. [ gunfire ] >> there are explosions and gunfire going on down the street. [ gunfire ] we have a press conference now getting started.

we'll pick it up in progress. >> -- suspect consistent with the description of suspect number two, the white cap individual who was involved in monday's bombing of the boston marathon. we have a picture, a video, from the 7-eleven last night that he's dressed in a grey hoodie-type sweatshirt, light skin, caucasian male, with long, brown, curly hair. that's the individual that we're looking for at this moment. >> that's suspect number two? >> yes. >> suspect number one was shot? >> yes. >>. >> i want to be clear, we'll do regular updates to this. but right now, we're in a public safety mode now. our immediate concern is for those people in that neighborhood up there, we have an activer is going on by

tactical teams to aprehend this particular individual, he should be considered armed and dangerous. so, please, use extreme caution and stay in your homes. if you hear something, you see something unusual, we would like you to call 911. we'll describe the area, the neighborhoods and 2 streets that are involved up there so everyone is clear on that. >> wait a minute. what is your name. >> i'm calling on the watertown community to be calm during this time. we're talking about east watertown, dexter street, school street areas, to remain in your homes. we'll be doing a search, please stay in your homes, do not come out, if you get a knock on your door, make sure we'll have yuan formed officers there to assist with the screening and safety of

these communities. watertown has always been very good. >> there will be control blasts of some kind at east watertown. >> no. not at this time. teams have been up there in the process of recovering that was discharged from those vehicles. >> sir, do you now how many? >> we're not prepared to talk about identifications. that's one of the reasons those videos were released earlier yesterday. i'm not getting into specifics about that. we don't have the names at this point. >> listen, this is an ongoing investigation. we can't get into details on the description of the suspects or the names. we're trying to get information out to the people who live here, they should stay in their homes

and not open their doors unless police officers are there. there's a 20-block perimeter of the area that the chief devoe just spoke about. we believe that this to be a terrorist, a man who's come here to kill people. we need to get him in custody. one thing that i want to say is there have been two police officers, one killed and one badly injured. our sympathies go out to chief mcmillan and to the families of those officers. this is a terrible tragedy. we don't want to increase it. we want to be very careful of what we do. >> folks, we got to get back in incident. we'll be back in about an hour to brief you again. thank you. >> you have been listening to an impromptu -- >> remarkable developments overnight in the case of the boston marathon bombing.

you're hearing from law enforcement officials in boston, massachusetts, one of the suspects has been killed in a firefight that took place with police last night. at least another suspect is at large, the one that was referred to suspect as number two in those photos that were released by law enforcement yesterday. he was the one wearing the white cap, he's believed to be armed and dangerous and that the public should use extreme caution, the quote that one of the officers there said that we believe this is to be a terrorist, this we believe this is a man who has come to kill people. also, the toll from the evening, one police officer, one m.i.t. campus officer was killed overnight. one officer dead in activity that took place related to all of this. that's how all this all began to unfold last night on the campus of m.i.t., followed reports of

gunfire in watertown, an eyewitness saying there were explosions, three straight explosions and gunfire, there was an extensive firefight between these two suspects and police officers and during the course of that firefight, they released some explosives, they threw what appeared to be hand grenades at the police officers and also, a pressure cooker bomb, which in fact, would be consistent to the device that was used in the marathon bomb blast. i would like to bring in, at this time, one of our reporters on the ground, a number of people on the ground in watertown, massachusetts. just to reiterate what is happening now, law enforcement just confirmed that one of the suspects is dead and one is at large. they started to answer some of the questions that we had all

night. we wanted to be very responsible in our reporting and didn't want to jump to conclusions. we weren't sure of the link between in cambridge, watertown and what happened earlier in the week at the boston marathon bombings. we didn't know if these were separate or just cases of urban crimes. we have more answers to that. again a press conference just held by law enforcements massachusetts police confirming that one suspect is dead and one suspect remains at large. apparently they have some video from 7-eleven in cambridge. lot of activity overnight. we're still trying to piece together how it fits together. reports of armed robberies overnight, including one at a 7-eleven.

from the press conference, they said they referenced some surveillance video from 7-eleven in cambridge, that they had video of suspect number two, they described as a light-skinned call caution male, this is the suspect in those photos, released by law enforcement, this is suspect number two, the one who's wearing the white hat. they believe they have surveillance video of him at a armed robbery at a 7-eleven in cambridge yesterday. this is the gentleman they say is at large. this man is at large. he's armed and dangerous the public should use extreme caution. they have told people in the area to stay inside and not open their door. unless they can confirm that it's a police officer on the other side of it. saying, quote, we believe this to be a terrorist, we believe this is a man who has come to

kill people. . in fact, there was some loss of life, one officer was killed on the campus of m.i.t. this all started around 10:45 last night. that officer was responding to a report of disturbance when he was shot. we don't know what that disturbance was. again, i apologize for all of the unknowns. there was tremendous amount of criminal activity and violence overnight. we're still trying to figure out how it all fits together. there was an armed robbery. a shooting of a m.i.t. campus officer, and then all of this violence in watertown. i want to go to pete williams who can help us figure some of this out. >> reporter: earlier tonight on msnbc, client van zant a former fbi profiler, that this may have

started, they wanted to steal a car and get away, it appears from the facts that it had, that's exactly what happened here. this all started according to authorities when there was a shooting at the campus of m.i.t. by two men who then committed an armed car jacking in cambridge, massachusetts, they say that the owner of the car was held at gun point by two men, kept in the car for about a half-hour and then that victim was subseque subsequently released at a gasoline station at cambridge and was not hurt. then, the police purr pseudothat vehicle to watertown, during that chase, explosive devices were thrown from the car by the suspects. we believe at least one pressure cooker bomb was thrown at that point, according to authorities.

during that shootout, one of the suspects was killed and the other is now at large. the two suspects, we have now heard, from a multiplicity of law enforcement officials are the two men that the fbi said committed the bombing in boston. the man that's been killed was the one shown in the pictures wearing the black hat. the one is at large is the one who was shown in the white hat. set the bomb at the restaurant the second bomb. the person you're looking at now is the one that's considered at large, armed and dangerous. >> pete, that information that you just provided sheds a lot of light on what we have seen overnight. lot of activity in subsequent fashion. we didn't know how it was linked. do we know how the m.i.t. campus

officer factored into this the, how he ended up being shot and killed? >> no, it's not clear. it may be that they were responding to a report of a theft. and that he was shot, so, obviously, these two men not only have bombs, they have also have guns, they used tonight to kill one policeman, injure a second, perhaps, seriously, before one of them was killed in the resulting exchange of gunfire. >> all right, pete williams, live in d.c. and that actually, as someone who's been covering this story since about 10:45 last night, since it all started your information helps an awful lot. so, that's some very universal information and piecing together the narrative here. if we could bring clint in, i want to bring our viewers up to

speed on the very latest. an awful lot of developments in a very short period of time and it seems that we are now just able to make some sebs of it. it started last night with the shooting on the campus of m.i.t., around 10:45, m.i.t. campus police officer was responding to a report of disturbance where he was shot multiple times and killed. there was a car jacking in cambridge around that time. that the two suspects in the boston marathon bombing car jacked a gentleman and then began a police chase, that led to this shootout in watertown, this exchange of gunfire, where during that time, the suspects also threw explosives at officer. the one of the suspects is dead. one of them remains at large and police are warning the public that he is armed and dangerous and they're to use extreme caution in this manner.

people should stay in doors unless they can confirm that a police officer is on the other side of that door. i want to go now to nbc news' lester holt, live on the ground in watertown, les zbler mara, we're standing at the edge of the perimeter, 20-block perimeter, you heard the police and authorities here are warning people to stay inside, that one suspect, suspect number two, the white-hat suspect is still at large, they're telling people do not answer your door if there's a knock at your door, obviously, unless it's police, they don't know where this individual is, he apparently drove out of that shootout, crashed through the police barricade, they still believe that he's still in this perimeter, it's still a very active and dangerous crime scene, you'll recall during the press conference last night,

they noted they thought they were armed and dangerous beyond the capability to create bombs. police certain certainly dealt with both tonight during that chase the suspects apparently throwing explosive devices out at them and the gunfire, they apparently were armed with quite a bit of fire power. people in that part of watertown being told to stay indoors right now. this is still a very active scene here, still a very dangerous place, with a person who has apparently accused of planting the bombs along the marathon route and firing at police tonight. also involved in the shooting of that m.i.t. police officer, they believe, who was shot and killed. another transit officer was wounded during the pursuit. this is a very, very volatile

scene right now. again, we have heard these two individuals are in fact the individuals wanted for the marathon bombing. this all apparently coming to an ahead here tonight. authorities weren't trying to execute a raid here of any kind. this is an outgrowth of that shooting at m.i. . what were they doing at m.i.t.? police never made it out of his vehicle, he was shot inside his vehicles. they apparently wouldn't on to a car jacked the vehicle. kept the owner in the vehicle for about a half-hour, before kicking that individual out. very tense scene here, mara. >> lester, you make a very good point and one that pete williams has made a point to repeat several times this evening, this didn't start with a police action, officials released the

photos of those two men yesterday. everything that happened overnight, wasn't because they were able to locate them or aprehend them, this apparently started with a crime by the two suspects. we were talking to fbi profiler, one of this things was a possibility, looking to get out of a town in a car that wasn't linked to you is to car jack someone and it appears that's what happened. i would like to go to clint at this time. clint, your predictions have proven to be true in this case, at least, as you have heard all of these developments, given your 25-plus years of experience as a law enforcement officer, what do you make of all of this? >> it's an active investigation

the release of the photographs has proved to be what is very critical in this case, i think the fbi and other agencies had those pictures for about 24 hours. they tried very hard to identify those suspects themselves. they would have to identify the suspect, locate them in one place, conduct a surveillance and then make an arrest, the last thing they wanted to get involved in was a moving situation, a shooting situation, nonetheless, that has happened, that's the cards that have been dealt to law enforcement and that's what they're dealing with. and one question i have, i have seen photographs, pictures, videos tonight of at least one individual totally stripped of all of his clothing in custody of law enforcement and we have

been told that one of the suspects is shot and dead and one of the suspects is a fugitive, there appears at least a third person somehow has come into this equation and law enforcement felt that that individual, that man, was a significant enough threat that he was stripped of all of his clothing before he was handcuffed and placed into a police vehicle, lot of unanswered questions still and what we don't know is, do we just have these two and one individuals or anyone else giving them aid and comfort. >> clint, touch upon the threat of the public from this suspect number two, police have been very clear, the they spoke so plainly, we believe this is a man who has come here to kill people. can you speak to the threat to the public right now?

>> well, the individual, the one in the white cap, he appears to be the younger of the two, realize, the fbi identified them suspect one, suspect two the individual as you just showed right here wearing the white baseball cap, he appeared in the videos that we saw yesterday, not only to be the younger but perhaps to be the less dominant, in essence, he was the one following the other person. he's the one that's on the run right now and he's also the one who was believed to have e been seen in photographs of placing the device now. the threat to the public, should he still not in police custody, they have shown, they'll exchange gun fist, they have shown they'll car jack and take

hostages. it's very likely that this person on the run, if he can't get his hands on another vehicle, he's likely to break into some building or some residence and try to find shelter and wait out the law enforcement response. the threat is very real to the public. law enforcement is not only trying to people out of their way but to keep them alive by telling them to stay in their houses, keep your doors locked. >> of course, people have to go on with their lives, as morning brokes here, this is a very serious situation, we saw what these people are capable of what with these two bombings that happened earlier in the week, killing three and injuring 170. what should people do this morning? should stay at home?

>> i think they'll have to follow the news very closely, realize that law enforcement by some estimates has a 20-block area isolated where they believe or suspect that this second individual, subject number two, may be located. if that's the case, they'll be doing a house by house, car by car, building by building search that's going to be extremely manpower intensive. believe that the law ens are fomt, if they don't have this individual in custody, they'll have to set up roadblocks and checking the inside of cars. again, with the idea that there may have been another car jacking as this individual attempts to flee this area, we not only have a very dangerous person but we have a fugitive on the run who is in his own mind may believe that he has nothing to lose. if he's watching your broadcast

right now, this is the time for this person not to die but this is the time if he has a reason why he was involved in these bombings whatsoever, this is the time to turn himself in to authorities and make that statement. otherwise, they both will die in this situation and whatever they did this for will not be known, if they wanted it to be known, if the survivor in the white cap you're showing right now, if he wants his motive to be known and understood, the only way it's going to happen is to contact the authorities, turn himself in and make a statement. >> we know now a number of things about this individual, we know that he participated in the planning and execution of a bomb attack at a major public event, where there were a number of attendees at the boston marathon there, we know that he engaged

in this car jacking. we know that he exchanngaged th a firefight. based on what we know about this individual and his criminal activity, as a former profiler, what can you tell us about this kind of person? >> well, this is someone who has engaged in meticulous planning as far as the actual event, the building of the device, they have allegedly assembled grenades, weapons, pressure cooker bombs, one of which was supposedly thrown at authorities and detonated tonight. it takes time to accumulate guns, weapons, explosives and the ability to build this, so all of this took a significant amount of time. it looks like right now what they may have not put a whole

lot of time is, is their plan to escape, apparently, their escape plan was hunker down and see if they could ride it out. i think what made the difference and what makes a difference in a case like this in the 21st century and the technology to isolate these photographs. >> all right, former fbi profiler clint van zant. we just want to bring viewers up to speed on where things stand right now. a number of developments. a tremendous amount of activity over the course of the last few hours and here's where things stand at this time. one of the suspects in the boston marathon bombing is dead at this time. one of suspects at large. that suspect was referred to as suspect number two, shown in photos wearing the white cap and fishlts say that he's believed to be armed and dangerous. they're advising the public to use extreme caution and advising

massachusetts residents to stay indoors and not answer their doors. a human toll here, one police officer was killed overnight in a shootout with this man. story. stay with us for more. good morning. lester holt in watertown, massachusetts, after a dramatic night, the two men suspected of carrying out the marathon bombing in boston on monday have apparently led police on a wild chase, a shootout. this morning, one is dead, another is at large. place here in watertown telling people to stay in their homes, do not answer the doorbell.

one of the suspects, after engaging in a wild chase and a dramatic shootout here tonight. this all began last evening in cambridge, massachusetts, at the campus of m.i.t., when a police officer investigating a distu disturbance was shot and killed. the two suspects then carjacked a vehicle, according to police, led them on a chase here to watertown, throwing explosives out at the officer, we're told. then that ensued into a prolonged exchange of gunfire into which one of the suspect was killed. authorities, again, tell us these two men are the same ones identified in the photographs yesterday released by the fbi. nbc's pete williams is standing by now in our washington bureau with more. pete, what more can you tell us? >> well, quite a bit more, lester. we're learni ining much, much m about this. the person who was killed tonight was the man who was identified by the fbi at the

thursday evening news conference as wearing the black hat. the man who is at large is the one they've identified as wearing the white hat, who they believe set the second bomb. now, according to police, as you say, this started not because the fbi was about to arrest them, but because they apparently, feeling the pressure, were trying to get away and began by ambushing a cambridge policeman. they then robbed a 7-eleven and carjacked someone. that led to watertown. when they got to watertown, the car stopped in which they were driving. the man with the black hat got out. police say that he was carrying a weapon of some kind they're not sure exactly what it is at this point. and he had some kind of improvised bomb strapped to his chest. as the chase was going on, the two men were throwing bombs and grenades out the window. so there are undetonated explosives along this trail that

led from cambridge to watertown. the man with the white hat is at large. they're trying to find him now. and they're trying to identify these two. they believe they know who they are. they're trying to get a positive identity on them now, but we've heard from a couple of sources that the two may have overseas military backgrounds. if it is who they think it is, whom they strongly suspect it is, they have both been here for about a year. so they're not -- it would appear, not american born, but people who have come here. one of the boston authorities said tonight that one of these was a man who came here to kill people. so it seems like a growing belief here that these people did come here from overseas. so unknown suspect two, the man you're looking at now, is the one who's at large. they're trying to find him now. they say that if they can't find him, they may shut down the transit systems in the area and

shut down access into communities, if they can't find him. there's an all-out search. they're telling people to stay in their homes and keep their doors locked. but the main point here, lester, is that these two men who were accused of the boston bombing panicked earlier tonight trying to flee before anyone even made an attempt to arrest them, and brought this all on themselves, lester. >> and i'm standing here at the edge of a 20-block perimeter that police have established. they had made an announcement to the press about a half hour ago that this is a public safety issue right now as they issued a plea to residents on the east end of this community to stay indoors because this suspect is at large. here's a little bit of what police told the press just a short time ago. >> the pursuit went into a residential neighborhood not far from here where there was an

exchange of gunfire between watertown police and two suspects in this suv. they're in the course of that pursuit. several explosive devices were discharged from the car at the police officers. in the exchange of the gunfire, we believe one of the suspects was struck and ultimately taken into custody. a second suspect was able to flee from that car, and there is an active search going on at this point in time. >> let me go to nbc's michael isikoff. you heard pete williams mention a moment ago that police now suspect these two men have an overseas connection, may be foreigners. how does this change this story as we see it? >> well, right now i think everybody's focused on the man hunt for suspect number two, the man with the white baseball cap.

they have not released his identify. i think we should probably be a little cautious at this moment about the implications of that and just focus on what we're learning. we're getting some fresh details right now. i just got an e-mail from the district attorney in middlesex county that adds a bit to that police briefing, and if i could share it. this began at about 10:20 p.m. last night. we were previously told it began with a robbery of a 7-eleven by these two suspects. that was followed by reports of shots fired on the m.i.t. campus. an m.i.t. campus police officer was found shot in his vehicle. at that point, the two suspects actually engaged in a carjacking of a black mercedes suv. there was a victim in that. they took the victim with them. the victim whose suv was

carjacked was held at gunpoint and kept in the car with the two suspects for approximately half an hour. he was then released at a gas station on memorial drive in cambridge. the suv then drives to watertown. a police chase ensues, and during the chase, at that time, explosive devices were thrown by the suspects from the car. the suspects and the police officer exchanged gunfire. during this pursuit, an mbta transit officer was wounded and is now hospitalized. and it was also during that pursuit one of the suspects was critically wounded, taken to the hospital. he's now dead. the other suspect, the man with the white baseball cap known as suspect number two in the boston marathon bombing, escape d and e is at large. he's the man police are looking

for right now. >> michael isikoff, thank you. they're looking for him inside this 20-block area that extends from where we are deep into the city. again, residents on alert, being told not to answer their doors. if someone comes to their door, they're asked to call 911. we should note, s.w.a.t. teams are methodically working neighborhoods. the clouds have moved in here, and we're told federal authorities they cannot bring in their helicopters to conduct an aerial search. so they're somewhat hampered by the weather as they continue to try to hone in on this other suspect. again, the man you've seen in the white hat in that photo released by the fbi. we'll have continuing coverage on msnbc. also, more ahead on a special edition of "today" here on nbc. for now, i'm lester holt, nbc news.

i'm mara schiavocampo in new york with break news related to the boston marathon bombing. police say that one of the two suspects has been killed in a shootout with law enforcement. the second suspect remains at large and is armed and dangerous. they are warning the public to use extreme caution going as far as to tell massachusetts residents to stay indoors and to not open their door unless they can confirm that the person on the other side is a police officer. you are looking at the picture of that man. suspect number two, who is at large at this time. police saying, quote, we believe this to be a terrorist. we believe this to be a man who has come to kill people. a number of developments have taken place over the last few hours. this is a very fast-moving story. i want to go now to nbc news correspondent michael isikoff, who is live on the ground in watertown, massachusetts, with the very latest on this

developing story. michael, what can you tell us? all right. it appears we don't have michael isikoff ready. but we're looking at video of what happened last night. i want to bring you up to speed on what took place and what we now know. it all began around 10:45 yesterday evening when there were reports of a shooting at the campus of m.i.t. in cambridge, massachusetts. that's just outside of boston. officials say an m.i.t. campus police officer was responding to reports of a disturbance when she was shot multiple times. he was taken to the hospital where he was pronounced dead. there were no other victims in that case. officials now believe that around that same time those two suspects whose photos were released yesterday by law enforcement as the suspects in the boston bombing case, officials believe those suspects carjacked someone around that same time in cambridge and then led police on a chase through the towns of that area. they stopped in watertown where

they began to shoot at one another. they engaged in a lengthy fire fight. it was during that time that the suspects began throwing explosives at the officers. we spoke to one eyewitness earlier this evening who saw the whole thing from his apartment window. he says that they were throwing what appeared to be hand grenades and even a pressure cooker bomb. i want to bring this sound up if we can for just a minute. this is video of that fire fight. [ gunfire ] >> there's explosions and gunfire going on down the street.

[ gunfire ] >> a hail of gunfire there. we now know that was exchange between the two suspects in the boston bombing case and police who were on the scene. those two men also threw explosives at officers. one eyewitness said he saw what looked like a pressure cooker bomb, which would in fact be consistent with the explosive that was used within the boston marathon on monday. three people were tragically killed in that attack. 170 were wounded, including many that were so severe they included limb amputations. i want to bring in nbc's kerry sanders, who is live in watertown. he's been on this story all night, starting in cambridge, massachusetts, with that shooting. kerry, good morning. >> reporter: yes, i'm now removed from a spot i had been

earlier. the officers asked us to back off because their concern was we were in an area where we could be in danger. they've moved us back considerably from where we had been. we were right at the location where that gunfire that we were just listening to had taken place. the officers were very suspicious of two, what they called, devices they found in the street. they actually brought in an armored personnel carrier to, i believe, put there sort of as a blast wall just in case those devices were to be bombs that exploded. at the same time, officers were moving behind houses in line looking for the possibility the suspect is somehow crouching in the darkness behind one of the houses. so they're moving behind houses, and they're telling all residents to remain indoors. as you can imagine, there's a lot of residents who are awake right now peering out of windows or sitting there watching

television and at the same time looking back and forth to see what's going on. the area where i am now, i've come just out of what i would say the officers were referring to as the hot zone. where i am right now, on the way out, i met a young woman. she told me she was a witness to the shootout. she was starting to explain to me the barrage, the hail of gunfire, when one of the officers saw me just sort of standing there talking to her, and that officer put his hand on his glock, which is a .9 millimeter, starting yelling at me, get your hands out of your pockets, it's cold out here. he's like, who are you, what are you doing, do not move. so earlier, we saw officers with tension. it has certainly dropped. at that point, he said, look, i know you're trying to do your job. i'm going to have to ask you to get out of her. don't talk to her right now, this witness. she's somebody we want to preserve for the moment. so i've